The present invention relates to the field of electrical machines, and more particularly a stator winding bar.
Alternating current machines use Roebel bars for the armature winding. Roebel bars consist of insulated strands that are arranged on top and next to each other and transposed. The transposition patented by L. Roebel in 1912 provides a full turn in the active part (360xc2x0 transposition). In the end zones (end winding), the bar is not transposed. This type of transposition compensates the field along the active part. However, it does not compensate the field components of the end winding.
Since then, many additional possibilities of transposition in the active part and end zones have been described and used. U.S. Pat. No. 3,118,015 to Willyoung describes an entire group of transpositions. This makes it possible to infinitely vary the transposition angle in the active part between 360xc2x0 and 720xc2x0 while preserving the full compensation of the slot field. The transposition of the active part is composed as follows: A middle part arranged symmetrically to the machine center, in which the crimping distances correspond to the 360xc2x0 standard transposition is provided with two border zones that have crimping distances with half the length of those of the middle part.
A well-known type of transposition constructed in this way is the 540xc2x0 transposition as described in U.S. Pat. No. 2,821,641 to Ringland. The middle part extends over half of the active length and therefore has a transposition angle of 180xc2x0; the border zones extend over a quarter of the active part length each and as a result of half of the crimping distances therefore also have a 180xc2x0 transposition. This adds up to a total transposition of 540xc2x0. This type of transposition compensates the field along the active part and compensates the external field of the end winding. The end winding inherent field in contrast is not compensated. Inherent field here means a field that changes in sinus shape over time and is positioned transversely to the bar side, and whose amplitude extends proportionally over the bar height in relation to the bar center (bar center: field remains zero, top bar edge: maximum field, bottom bar edge: same maximum field, reversed plus or minus sign). The external field accordingly is a field that changes in sinus shape over time that is positioned transversely to the bar side and remains in phase in relation to the bar height (constant field over bar height at a point in time).
Another transposition within the scope of the teaching of Willyoung""s patent is the 450xc2x0 transposition. The middle part hereby extends over xc2xe of the active partial length (270xc2x0 transposition), the border zones each extend over xe2x85x9 of the active partial length and each have a 90xc2x0 transposition. This type of transposition compensates the field along the active part and compensates the end winding inherent field relatively well. The external field of the end winding in contrast is only partially compensated.
In principle, it can be said that all possible transpositions according to Willyoung never compensate all effects of the end windings; a remainder of the inherent or external field always remains uncompensated.
It is the objective of the invention to create a stator winding bar in which, for the 450xc2x0 transposition in the active part, the external field of the end winding is largely compensated, and the circulating currents therefore are practically reduced to very small values.
An important aspect of the invention includes increasing the proportion of the middle part with respect to the length of the active part while preserving the same overall transposition and dividing the overall transposition over the middle part and border zones of the active part. As a result, additional induction surfaces for the external field are provided within the conductor loops of the stator winding bar in the middle part, which induction surfaces compensate the induction surfaces in the end windings without substantially changing the other compensations.
In particular, the middle part is extended in length to such an extent xc2xe over the total length of the active part that the resulting additional induction surface for external fields approximately equals the effect of the corresponding induction surface in the end windings (same flux linking).